The invention relates to a crankshaft milling apparatus having at least one milling unit with internal milling cutter means for the milling of the bearing or crank pins and flanks, especially of the crank bearings of a crankshaft. The milling unit is supported in or on a longitudinal slide which is movable on a longitudinal guide extending in parallel to the direction of the longitudinal axis of a crankshaft work piece. Further, the milling unit is tiltable or rotatable about a journal axis extending in parallel to the longitudinal work piece axis. Due to these features the feed advance movement of the internal milling cutter means takes place along a circular path about the crankshaft bearing pin to be milled. In this type of apparatus the crankshaft work piece is maintained in a stationary position during the milling operation.
German Utility Model Publication (DE-GM) No. 7,106,698 discloses a machine of the just defined type, especially in FIG. 5. In this prior art machine a pivot journal with a circular guide is arranged below the crankshaft work piece. The feed advance drive is installed below the circular guide. The inner milling cutter itself is mounted eccentrically in a circular disk by means of which the inner milling cutter is guided along a circular path around the crank pin to be milled. In this type of prior art milling machine the crank pin or bearing pin to be milled, and thus the crankshaft, were maintained stationary during the milling. However, it has been necessary to rotate the crankshaft between two milling operations in such a manner that the crank pin to be milled takes up a predetermined position. This prior art structure has not been reduced to practice in any commercially feasible way because its assembly did not provide any advantages whatsoever compared to similar prior art structures so that the disadvantages necessarily resulting from the tilting of the milling unit have not been acceptable. Such disadvantages especially involve the displacement of the crank pin center also in the vertical direction when an adjustment had to be made for a different crankshaft stroke.
On the other hand, U.S. Pat. No. 4,337,011 corresponding to German Patent Publication (DE-AS) No. 2,915,662 discloses a crankshaft milling machine in which the work piece is rotating during the milling operation. In such a machine the milling unit is tiltable about a tilting or journal axis extending in parallel to the axis of the work piece. This type of arrangement has solved certain problems successfully. However, it also leaves room for improvement.
Austrian Pat. (AT-PS) No. 286,067 discloses a numerical control for two separate feed advance drives which operate at right angles relative to each other in crankshaft milling machines. Such controls are also useful in connection with the present invention.
German Patent Publication (DE-OS) No. 2,419,554 discloses a crankshaft milling machine in which a slide carrying the milling cutters is guided in parallel to the longitudinal axis of a work piece. Such a slide carries a ring type tool or cutter which rotates around the stationary work piece and the cutting or milling edge of the tool faces radially inwardly. The tool slide is of the so-called cross type comprising two slide members displaceable relative to each in directions extending across the longitudinal work piece axis and at right angles to each other. The relative movements of these two slide members to each other are controlled or coordinated to each other by means of a numerical circular path control. The invention does not require that the two slide members must move at right angles relative to each other.
It is also known that crankshaft milling machines employing radially inwardly effective milling cutters have a number of advantages compared to crankshaft lathe type machines so that recently crankshaft milling machines with inwardly effective milling cutters have been used predominantly. However, since the inwardly effective milling cutter surrounds the tool completely, there are certain stability problems, as well as problems regarding the chip removal or rather problems resulting from the deposition of chips on the guide surfaces on which the milling unit is moving, as compared to older milling machines for crankshafts.
The stability problems are due to the fact that it must be possible to completely withdraw the milling unit from the work piece zone. To achieve this purpose the vise chuck components for holding the work piece were so constructed that the chuck proper was mounted on a neck projecting from the vise in the direction of the work piece axis. For this type of construction it is necessary that the spacing between the chuck proper and the vise is dimensioned corresponding to the extension of the milling unit including the carrier means for carrying the milling unit in the direction of the work piece axis. On the other hand, the vise neck for carrying the chuck must have a diameter as small as possible, in any event it must be smaller than the effective diameter of the inner milling cutter. As a result, it cannot be avoided that such vise neck has only a limited stability. Such limited stability in combination with a relative unstable work piece, such as a crankshaft, required rather expensive supporting features and without such expensive supporting features prior art machines have been limited in their capacity.
It is also known to protect the guides or guide surfaces against falling down chips by cover means. However, such cover means do not remove or solve the basic problem that guide surfaces are present on which falling down chips may be deposited which is undesirable.